A “Time-of-Flight Mass Spectrometer” (TOF-MS) is a type of device used for performing a mass analysis by measuring the time of flight required for each ion to travel a specific distance and converting the time of flight to the mass. This analysis is based on the principle that ions accelerated by a certain amount of energy will fly at different speeds corresponding to their mass. Accordingly, elongating the flight distance of ions is effective for enhancing the mass resolving power. However, the elongation of a flight distance along a straight line requires an enlargement of the device. Given this factor, Multi-Turn Time-of-Flight Mass Spectrometers (Multi-Turn TOF-MS) have been developed in which ions are made to repeatedly fly along a closed orbit such as a substantially circular shape, substantially elliptical shape, substantially “8” figure shape, or other shapes, in order to simultaneously achieve the elongation of the flight distance and the downsizing of the apparatus (refer to Patent Documents 1 and 2, and other documents).
Another type of device developed for the same purpose is the multi-reflection time-of-flight mass analyzer, in which the aforementioned loop orbit is replaced by a reciprocative path in which a reflecting electric field is created to make ions fly back and forth multiple times and thereby elongate their flight distance. Although the multi-turn time-of-flight type and the multi-reflection time-of-flight type use different ion optical systems, they are essentially based on the same principle for improving the mass resolving power. Accordingly, in the context of the present description, the “multi-turn time-of-flight type” should be interpreted as inclusive of the “multi-reflection time-of-flight type.”
As previously described, a multi-turn time-of-flight mass spectrometer can achieve a high level of mass resolving power. However, it has a drawback due to the fact that the flight path of the ions is a closed orbit. That is, as the number of turns of the ions increases when they are made to fly along the closed orbit, an ion having a smaller mass and flying faster overtakes another ion having a larger mass and flying at a lower speed. If such an overtaking of the ions having different masses occurs, it is possible that some of the peaks observed on an obtained time-of-flight spectrum correspond to multiple ions that have undergone a different number of turns, i.e. traveled different flight distances. This means it is no longer ensured that the mass and the time of flight uniquely correspond, so that the time-of-flight spectrum cannot be directly converted to a mass spectrum.
Because of the aforementioned problem, in conventional multi-turn time-of-flight mass spectrometers, ions are selected in advance among the ions that originate from a sample generated in an ion source so that their mass is limited to a range where the aforementioned overtaking will not occur. The selected ions are made to fly along the loop orbit to undergo a predetermined number of turns and then be detected. Although a mass spectrum with a high mass resolution can be obtained with such a method, the range of the mass spectrum is significantly limited.
Patent Document 3 and other documents propose a method for performing a data processing function in which the results obtained by performing a plurality of mass analyses of the same sample under different conditions are compared to deduce the number of turns of the peaks appearing on a mass spectrum. However, this method requires the same sample to be mass analyzed plural times. Hence, the measurement takes a long time, and the amount of the sample is required that much.    [Patent Document 1] JP-A 2006-228435    [Patent Document 2] JP-A 2008-27683    [Patent Document 3] JP-A 2005-116343